The interaction of viral and host gene products can significantly influence the outcome of viral infection, which can be survival, life-long persistent infection, oncogenesis, or death. Adenoviruses cause 3-7% of respiratory illness in adults and young children and are associated with acute pneumonia in children in developing countries, where they are a significant cause of illness and death. Immune suppressed pediatric bone marrow transplant recipients are particularly at risk for adenovirus infection and mortality. Adenovirus infections are a problem in young, healthy military recruits, and a virulent serotype has recently emerged in the general population. However, study of human adenovirus pathogenesis in animal models is limited by species-specificity. The long-term goal is to elucidate the molecular basis of pathogenesis of an adenovirus, mouse adenovirus type 1 (MAV-1) that can be studied in its natural host. The objectives of this proposal are to (a) understand how viral attachment and entry impact pathogenesis, and (b) identify the interactions of viral early gene products and host gene products that affect the innate immune response. The emphasis is on in vivo assays, to provide validation of models of adenovirus-host interactions and pathogenesis that have been based on in vitro research with human and animal adenoviruses. Available tools that will facilitate these studies include viral and mouse mutants and immunological and molecular reagents. The specific aims are: Aim 1. Identify how virus-receptor interactions impact MAV-1 infection. Wild-type and mutant viruses and mice will be used to determine whether receptors identified in studies in vitro function in mice, and how receptor usage contributes to pathogenesis. Aim 2. Identify the mechanisms by which MAV- 1 activates innate immune responses. The extent to which MAV-1 triggers innate signaling pathways for dsDNA in the endosome (TLR9) and cytosol (TBK/IRF3 and inflammasome) will be assayed. Aim 3. Determine how MAV-1 infection breaks down the blood-brain barrier and causes encephalitis. Virus mutants will be used to determine the known or new signaling pathways that are used by the virus to disrupt brain endothelial function and cause inflammation. This research will provide important fundamental knowledge about adenovirus-host interactions in a tractable animal model. A thorough knowledge of adenovirus basic biology is critical for the development of safe antiviral drugs, adenovirus-based gene transfer vectors, and vaccines.